MSK investigations help in diagnosing, monitoring disease activity, and assessing progression, but they should always be used along with clinical examination.
Mnemonic: "D.R.I.M.S. =
Diagnosis, Response to Treatment, Inflammation, Monitoring, Structural
Changes"
1. SYNOVIAL FLUID ANALYSIS
Most Important Test for:
- Septic
Arthritis → Bacterial infection in joints.
- Crystal
Arthritis → Gout (Monosodium Urate Crystals) & Pseudogout (CPPD
Crystals).
- Hemarthrosis →
Bleeding into joints (Trauma, Hemophilia).
Findings:
- Septic
Arthritis → Cloudy, ↑ WBCs, Bacteria on Gram Stain.
- Gout → Needle-Shaped,
Negatively Birefringent Crystals.
- Pseudogout → Rhomboid,
Positively Birefringent Crystals.
Mnemonic: "S.G.H. =
Septic, Gout, Hemarthrosis"
2. IMAGING INVESTIGATIONS
A. X-RAY (First-Line for Bone
& Joint Conditions)
Findings:
- Osteoarthritis
(OA) → Joint Space Narrowing, Osteophytes.
- Rheumatoid
Arthritis (RA) → Marginal Erosions, Joint Deformities.
- Gout →
Punched-Out Erosions ("Rat-Bite" Lesions).
- Ankylosing
Spondylitis → Bamboo Spine (Fusion of Vertebrae).
Mnemonic: "O.R.G.A. = OA,
RA, Gout, Ankylosing Spondylitis"
B. BONE DENSITY TEST (DEXA SCAN)
Used for:
- Osteoporosis (Measures
Bone Mineral Density – BMD).
- T-Score
< -2.5 = Osteoporosis, -1 to -2.5 = Osteopenia.
Mnemonic: "D.O. = DEXA
for Osteoporosis"
C. MRI (Soft Tissue & Early
Changes)
Best for:
- Early
Rheumatoid Arthritis (Detects Synovitis Before X-ray Changes).
- Disc
Herniation (Nerve Compression).
- Avascular
Necrosis (Hip & Shoulder Bones).
- Soft
Tissue Injury (Ligament Tears, Rotator Cuff Tears).
Mnemonic: "M.R.A.S. = MRI
for RA, Avascular Necrosis, Spine, Soft Tissues"
D. CT SCAN (3D Bone Details)
Best for:
- Complex
Bone Fractures.
- Tumors
& Bone Metastases.
- Spinal
Canal Narrowing (Spinal Stenosis).
Mnemonic: "C.T. = Complex
Trauma"
E. ULTRASOUND (Soft Tissues &
Fluid Collections)
Used for:
- Joint
Effusion (Fluid in Joints).
- Tendinitis
(Achilles Tendon, Rotator Cuff).
- Baker's
Cyst (Swelling Behind Knee).
Mnemonic: "U.L.T. =
Ultrasound for Ligaments & Tendons"
3. BLOOD TESTS FOR MSK DISEASES
A. INFLAMMATORY MARKERS
- C-Reactive Protein (CRP) & ESR → Elevated in RA, Gout, Infections.
- Normal in Lupus Despite Active Disease.
Mnemonic: "C.E.L. = CRP
& ESR for Lupus Exception"
B. AUTOIMMUNE MARKERS
- Rheumatoid Factor (RF) → Positive in RA but Not Specific.
- Anti-CCP → More Specific for RA (Early Diagnosis).
- Antinuclear Antibody (ANA) → Positive in Lupus (SLE).
- HLA-B27 → Positive in Ankylosing Spondylitis & Reactive Arthritis.
Mnemonic: "R.A.A.H. = RF,
Anti-CCP, ANA, HLA-B27"
C. METABOLIC & OTHER TESTS
- Uric Acid → Elevated in Gout.
- Creatine Kinase (CK) → High in Myopathy & Muscle Damage.
- Calcium, Phosphorus, ALP → Bone Diseases (Osteomalacia, Paget’s).
Mnemonic: "U.C.C. = Uric
Acid, CK, Calcium for Metabolic Bone & Muscle Issues"
4. OTHER SPECIALIZED TESTS
- Electromyography (EMG) → For Neuromuscular Diseases & Myopathy.
- Muscle Biopsy → Confirms Muscular Dystrophy & Myositis.
- Bone Biopsy → Osteomalacia & Bone Tumors.
Mnemonic: "E.M.B. = EMG,
Muscle Biopsy, Bone Biopsy"
FINAL REVISION WITH MNEMONICS
- Purpose = "D.R.I.M.S." (Diagnosis, Response to Treatment, Inflammation, Monitoring, Structural Changes)
- Synovial Fluid = "S.G.H." (Septic, Gout, Hemarthrosis)
- X-ray = "O.R.G.A." (OA, RA, Gout, Ankylosing Spondylitis)
- DEXA = "D.O." (DEXA for Osteoporosis)
- MRI = "M.R.A.S." (MRI for RA, Avascular Necrosis, Spine, Soft Tissues)
- CT = "C.T." (Complex Trauma)
- Ultrasound = "U.L.T." (Ultrasound for Ligaments & Tendons)
- Inflammatory Markers = "C.E.L." (CRP & ESR for Lupus Exception)
- Autoimmune = "R.A.A.H." (RF, Anti-CCP, ANA, HLA-B27)
- Metabolic = "U.C.C." (Uric Acid, CK, Calcium for Metabolic Bone & Muscle Issues)
- Specialized Tests = "E.M.B." (EMG, Muscle Biopsy, Bone Biopsy)
